'\" te
.\"  Copyright 1989 AT&T
.\"  Copyright (c) 2006, Sun Microsystems, Inc.,  All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.TH PUTBQ 9F "Jan 16, 2006"
.SH NAME
putbq \- place a message at the head of a queue
.SH SYNOPSIS
.LP
.nf
#include <sys/stream.h>



\fBint\fR \fBputbq\fR(\fBqueue_t *\fR\fIq\fR, \fBmblk_t *\fR\fIbp\fR);
.fi

.SH INTERFACE LEVEL
.sp
.LP
Architecture independent level 1 (DDI/DKI).
.SH PARAMETERS
.sp
.ne 2
.na
\fB\fIq\fR\fR
.ad
.RS 6n
Pointer to the queue.
.RE

.sp
.ne 2
.na
\fB\fIbp\fR\fR
.ad
.RS 6n
Pointer to the message block.
.RE

.SH DESCRIPTION
.sp
.LP
The \fBputbq()\fR function places a message at the beginning of the appropriate
section of the message queue. There are always sections for high priority and
ordinary messages. If other priority bands are used, each will have its own
section of the queue, in priority band order, after high priority messages and
before ordinary messages. \fBputbq()\fR can be used for ordinary, priority
band, and high priority messages. However, unless precautions are taken, using
\fBputbq()\fR with a high priority message is likely to lead to an infinite
loop of putting the message back on the queue, being rescheduled, pulling it
off, and putting it back on.
.sp
.LP
This function is usually called when \fBbcanput\fR(9F) or \fBcanput\fR(9F)
determines that the message cannot be passed on to the next stream component.
The flow control parameters are updated to reflect the change in the queue's
status. If \fBQNOENB\fR is not set, the service routine is enabled.
.SH RETURN VALUES
.sp
.LP
The \fBputbq()\fR function returns \fB1\fR upon success and \fB0\fR upon
failure.
.sp
.LP
Upon failure, the caller should call \fBfreemsg\fR(9F) to free the pointer to
the message block.
.SH CONTEXT
.sp
.LP
The \fBputbq()\fR function can be called from user, interrupt, or kernel
context.
.SH EXAMPLES
.sp
.LP
See the \fBbufcall\fR(9F) function page for an example of \fBputbq()\fR.
.SH SEE ALSO
.sp
.LP
.BR bcanput (9F),
.BR bufcall (9F),
.BR canput (9F),
.BR getq (9F),
.BR putq (9F)
.sp
.LP
\fIWriting Device Drivers\fR
.sp
.LP
\fISTREAMS Programming Guide\fR
